Local Strain Triggers Polymorphic Phase Transformation in Layered Materials: A Case Study of Lead Oxide.

The ability to manipulate the crystal phase of 2D materials is a powerful lever for creating next-generation electronic and catalytic devices. However, controlling these nanoscale transformations requires a fundamental understanding of their atomic-scale mechanisms, which remains a significant challenge. This study directly addresses this by investigating local phase transitions in the polymorphic layered material lead oxide (PbO). Through atomic-resolution electron microscopy and simulations, we reveal that the material's characteristic structural patterns originate from localized orthorhombic domains formed by strain relaxation around crystal defects. We conclusively demonstrate this mechanism by externally inducing the same transformation with applied pressure. Our work firmly establishes strain engineering as a potent and predictable tool for designing nanoscale phase domains, providing a novel composition-preserving strategy to tailor the properties of advanced materials.